Method for producing low silicon ferromanganese alloys



United States Patent 3,374,088 METHOD FOR PRODUCING LOW SILICONFERROMANGANESE ALLOYS Henry Epstein, Bethlehem, and Victor AlfredNeubaum,

Coopersburg, Pa., assignors to Bethlehem Steel Corporation, acorporation of Delaware No Drawing. Filed Feb. '16, 1966, Ser. No.527,759 2 Claims. (Cl. 75-60) This invention in general relates to themanufacture of ferroalloys and in particular to the manufacture of lowsilicon ferromanganese.

For various metallurgical and operating reasons, steelmaking plantsrequire that standard high carbon ferromanganese used as an alloying ordeoxidizing agent in steel should contain not more than 0.25 silicon.

Ferromanganese alloying agents are commercially manufactured in either ablast furnace or in an electric furnace. The blast furnace product isusually high in carbon and usually high in silicon, i.e. over 0.50% byweight. In order to produce a low silicon ferromanganese alloy in theblast furnace, it is necessary to carefully select raw materials to makeup the charge. Usually a very low ash coke is used in the charge.Although carefully selected raw materials are used to manufacture thelow silicon ferromanganese alloys, the operation of the blast furnace iserratic, resulting in many missed heats, that is, ferromanganese alloyshaving over 0.25 silicon by weight. It is therefore erratic andexpensive to manufacture low silicon ferromanganese alloys by thisprocess.

Electric furnace melting offers a greater control of the final productthan does the blast furnace melting. However, electric furnacemanufacture of the low silicon ferromanganese alloys requires the use ofexcessive quantities of flux materials to prevent the loss of largeamounts of manganese to the slag and to prevent a high silicon contentin the final product. The two-step methods in which high silicon slag orferromanganese made in one furnace is subjected to a second,desiliconization step in a second furnace require specialized equipmentsuch as two electric furnaces to carry out such methods.

It is evident from the foregoing that prior methods of manufacturing lowsilicon ferromanganese alloys are both erratic and expensive.

It is, therefore, the object of this invention to provide an improvedeconomical process for manufacturing ferromanganese alloys which have asilicon content of about 0.25% or less.

Broadly, the improved process for producing a low silicon ferromanganesealloy includes continuously treating a substantially horizonally flowingmolten stream of ferromanganese alloy high in silicon with a gaseousoxidizing agent in a refining vessel to remove a portion of the siliconcontained therein.

In a more detailed description of the invention, molten ferromanganeseis melted in any suitable furnace such as a blast furnace and istransferred by any convenient method such as a ladle to a generallyelongated substantially horizontal refractory-lined covered trough. Themolten ferromanganese is fed into one end of the trough at a ratesufficient to maintain a substantially horizontal flowing stream whichmay be about 2 inches to about 8 inches in depth. Gaseous oxygen isblown onto the surface of the molten flowing stream through a lanceextending downwardly through the roof of the trough in a plane verticalto the longitudinal axis of the said trough. The lance is disposed at anangle of about 15 to about 45 to the vertical to effect a concurrent ora countercurrent flow of oxygen with respect to the molten stream. Thelance height is adjusted so that its nozzle is about 2 inches to about 8inches above the surface of the molten 3,3 74,088 Patented Mar. 19, 1968stream. We have found that by blowing oxygen in a volume of about 60cubic feet per minute to about cubic feet per minute and at a velocityof about 700 feet per second to about 1000 feet per second, a reductionof about 0.07% by weight to about 0.083% by weight of silicon may beremoved per lance from the molten ferromanganese. Accordingly, thenumber of lances to be used for desiliconizing a given batch offerromanganese will depend on the initial silicon content of the batchand the desired final content.

At no time during the process is a flux added to the vessel. Theformation of the siliceous manganese-bearing slag formed during thedesiliconization process provides an unexpected result in our process inthat he siliceous manganese bearing slag forms a glassy, pebblyprotective film on the surface of the refractory lining prolonging thelife thereof.

In a specific example of the method of this invention, 92.5 tons of aferromanganese alloy having a chemical composition of carbon 6.9%,manganese 77.6% and silicon 0.41% were tapped from the blast furnace andwere fed at an average rate of 1.03 tons per minute to the refiningvessel in a stream which was 6% inches deep. The molten stream was blownwith oxygen supplied through three water cooled lances extendingdownwardly through the roof of the vessel at an angle of +30 to thevertical to effect a flow of oxygen countercurrent to the stream ofmolten metal. The lance tips were three inches above the surface of thestream. Oxygen at a velocity of 745 feet per second and a volume of 65cubic feet per minute per lance was blown onto the stream of flowingmetal to effect a removal of approximately 0.083% silicon per lance. Theferromanganese flowing out of the refining vessel was found to have achemical composition of carbon 6.90%, manganese 77.3% and silicon 0.16%,the remainder iron and incidental impurities.

In another example of the invention, 76.3 tons of a ferromanganese alloyhaving a chemical composition of carbon 6.8%, manganese 76.8%, silicon0.31%, and the remainder iron and incidental impurities were tapped froma blast furnace and were fed to the renfining vessel at the rate of oneton per minute in a stream 6% inches deep. Oxygen was blown onto thestream at a velocity of 760 feet per second and a volume of 6 cubic feetper minute per lance through two lances depending downwardly through theroof of the vessel at an angle of +30 to the vertical to effect a flowcountercurrent to the stream. The lance nozzles were three inches abovethe surface of the stream. Each lance removed approximately 0.080%silicon from the stream. The chemical composition of the refinedferromanganese was carbon 6.9%, manganese 76.5%, silicon 0.15%, theremainder substantially iron and incidental impurities. The oxygentreatment effectively removed 0.16% silicon from the molten blastfurnace ferromanganese alloy.

Although we have shown the preferred. embodiment of the invention andhave described it in a. clear and concise manner, it will be understoodthat other adaptations and modifications may be made without departingfrom the scope of the invention.

We claim:

1. A method of reducing the silicon content of a continuously flowingsubstantially horizontal molten stream of ferromanganese flowing througha trough, said stream being about 2 inches to about 8 inches deep,comprising blowing about 60 cubic feet to about 75 cubic feet per minuteof a commercially pure oxygen onto the surface of the flowing stream ofmolten ferromanganese at a velocity of 700 feet per second to about 1000feet per second through a lance, said lance being located in a verticalplane passing through the longitudinal axis of the trough 3 and beingdisposed at an angle to the vertical of about 15 to about 45 and havingits nozzle about 2 inches to about 8 inches above the surface of thestream.

2. A method as claimed in claim 1, said lance being at an angle of about+30 to the surface of the molten metal and having a nozzle 3 inchesabove the surface of the molten ferrornanganese, the depth of the streambeing v 4i about 6% inches, saidoxygen being blown at a velocity ofabout 760 feet per second in a volume of 65 cubic cubic feet per minute.

No references cited.

BENJAMIN HENKIN, Primary Examiner.

1. A METHOD OF REDUCING THE SILICON CONTENT OF A CONTINUOUSLY FLOWINGSUBSTANTIALLY HORIZONTAL MOLTEN STREAM OF FERROMANGANEE FLOWING THROUGHA TROUGH, SAID STREAM BEING ABOUT 2 INCHES TO ABOUT 8 INCHES DEEP,COMPRISING BLOWING ABOUT 60 CUBIC FEET TO ABOUT 75 CUBIC FEET PER MINUTEOF A COMMERCIALLY PURE OXYGEN ONTO THE SURFACE OF THE FLOWING STREAM OFMOLTEN FERROMANGANESE AT A VELOCITY OF 700 FEET PER SECOND TO ABOUT 1000FEET PER SECOND THROUGH A LANCE, SAID LANCE BEING LOCATED IN A VERTICALPLANE PASSING THROUGH THE LONGITUDINAL AXIS OF THE TROUGH AND BEINGDISPOSED AT AN ANGLE TO THE VERTICAL OF ABOUT 15* TO ABOUT 45* ANDHAVING ITS NOZZLE ABOUT 2 INCHES TO ABOUT 8 INCHES ABOVE THE SURFACE OFTHE STREAM.